1. Field of the Invention
The present invention relates to a leak inspection device in which air leakage from an object to be inspected is inspected with a leakage inspection medium (tracer gas) such as helium gas (He gas).
2. Description of the Related Art
Concerning prior art inspection methods to inspect a minute airtightness leak from an object to be inspected, an inspection method has been provided in which a helium gas leak detector to detect a volume of tracer gas (He gas), which has leaked out from an object to be detected, is used. An example of this inspection method is a vacuum type helium gas leak inspection method in which a vacuum chamber is used.
In the leak inspection device in which the vacuum chamber is used, an inspection is made according to the inspection flow shown in FIG. 2, which will be described as follows. A product, which is an object to be inspected, is accommodated in a vacuum chamber, and a pipe for charging He gas is connected to the product. Next, a vacuum pump is operated so as to discharge air from the vacuum chamber. When the degree of vacuum in the vacuum chamber has reached a predetermined value, for example, when the degree of vacuum in the vacuum chamber has reached 10 Pa, the vacuum pump is stopped so as to stop an air discharging operation and the product is filled with He gas supplied from a helium supply source. At this time, He gas is supplied until the pressure of He gas in the product is raised to about 1 MPa. Next, He gas, which has leaked out from the product into the vacuum chamber, is introduced into a leak detector and a volume of the leakage gas is measured by utilizing a mass spectrometry method. According to the result of the measurement, the quality of the product 1 is judged.
As described above, when the He gas leak inspection is made, the product is put into the vacuum chamber so as to make the inspection. However, in this case, in order to take the product in and out, the inner pressure of the vacuum chamber must be returned to the atmospheric pressure each time the product is taken in and out. At the time of returning the inner pressure of the vacuum chamber to the atmospheric pressure, as moisture is contained in the outside air introduced into the vacuum chamber, an inner wall temperature of the vacuum chamber is decreased by the adiabatic expansion caused by decompression. Therefore, the moisture contained in the outside air attaches to a surface of the inner wall of the vacuum chamber. Further, as the outside air enters the vacuum chamber at the time of taking the product in and out the vacuum chamber, the moisture contained in the outside air attaches onto the inner wall face.
After that, when air is sucked out from the vacuum chamber by the action of a vacuum pump so as to conduct a test on the product, the above attached water is evaporated again. As a result, it takes a long time to discharge air from the vacuum chamber. Further, the thus mixed water particles affect the mass spectrometry made by the leak detector, that is, the background of the measurement is raised, which deteriorates the measurement sensitivity.